1. Field of the Invention
The present invention relates to nuclear power plants, such as, without limitation, boiling water reactor (BWR) type nuclear power plants, and in particular to a system for mitigating potentially damaging noise and vibration caused by the excitation of standing waves in closed side branches of a nuclear reactor system such as a BWR system as a result of steam flowing through the main steam line of the system.
2. Description of the Related Art
A BWR comprises a reactor vessel partially filled with water coolant which serves as a heat transfer medium. A reactor core containing nuclear fuel that generates heat is surrounded by the water coolant. A plurality of “jet” pumps are disposed within the vessel for increasing the velocity of the coolant through the reactor core in order to efficiently remove the heat generated by the nuclear fuel in the reactor core. The heat generated by the nuclear fuel is taken-up by the surrounding water, which is vaporized by the heat to produce steam. A main steam line conducts the steam from the vessel to a turbine-generator to produce electricity in a manner well known in the art. After the steam passes through the turbine-generator, it is piped to a condenser for condensing the steam into liquid water. The condensed water is returned to the reactor vessel by means of a coolant feed pipe for replenishing the water vaporized by the heat of the nuclear fuel.
BWR type nuclear power plants can, at times, experience the excitation of acoustic standing waves in closed side branches off the main stream line (such as a standpipe including a safety relief valve) as a result of steam flowing through the main steam line. More particularly, as steam flows down the main steam line, vortex shedding across the opening of the closed side branch causes acoustic standing waves to be excited in the closed side branch at the resonant frequency of the closed side branch. These acoustic standing waves create pressure fluctuations that propagate through the main steam line and cause degradation to the steam dryer and other equipment on the BWR, such as safety relief valves and turbine stop valves.